test: add a test for table name starts with '_' case

For MySQL table name version.

test/unit/test_mrn_sys.cpp

@@ -106,6 +106,19 @@ namespace test_mrn_sys
     cut_assert_equal_string("@005fb", mrn_table_name_gen(arg4, buf));
   }
 
+  void test_mrn_table_name_gen_for_mysql()
+  {
+    char buf[64];
+    const char *arg1 = "./hoge/fuga";
+    const char *arg2 = "./foobar/mysql";
+    const char *arg3 = "./d/b";
+    const char *arg4 = "./d/_b";
+    cut_assert_equal_string("fuga", mrn_table_name_gen_for_mysql(arg1, buf));
+    cut_assert_equal_string("mysql", mrn_table_name_gen_for_mysql(arg2, buf));
+    cut_assert_equal_string("b", mrn_table_name_gen_for_mysql(arg3, buf));
+    cut_assert_equal_string("_b", mrn_table_name_gen_for_mysql(arg4, buf));
+  }
+
   void test_mrn_index_table_name_gen()
   {
     char buf[64], buf2[64];